I have read such a report a long time ago. It is said that scientists from Germany, Japan and other countries spent nearly 10 million yuan in five years to build a high-purity silicon-28 ball. This 1kg pure silicon ball requires ultra precision machining, grinding, polishing and precision measurement (ball surface, roughness, quality...) It's the roundest ball in the world. 

We often put grinding and polishing together, because the roughness of parts after these two processes has been very small. First, let's understand the difference between them.

The difference between grinding and polishing

Lapping is the finishing of the machined surface by the relative movement between the lapping tool and the workpiece under a certain pressure using the abrasive particles coated or embedded in the lapping tool. Grinding can be used to process all kinds of metal and non-metal materials. The surface shape of grinding includes plane, inner and outer cylindrical surface, conical surface, convex and concave spherical surface, thread, tooth surface and other surface. The machining accuracy can reach it5-it1, and the surface roughness can reach ra0.63-0.01 μ M.

Polishing is a kind of machining method that uses mechanical, chemical or electrochemical action to reduce the surface roughness of the workpiece, so as to obtain a bright and flat surface.

The main difference between the two is that the surface finish achieved by polishing is higher than that achieved by grinding, and chemical or electrochemical methods can be used, while grinding basically only adopts mechanical methods, and the abrasive particle size used is coarser than that used for polishing, that is, the particle size is larger.

Ultra precision polishing is the soul of modern electronic industry

The mission of ultra precision polishing technology in modern electronic industry is not only to flatten different materials, but also to flatten multi-layer materials, so that a few millimeter square silicon wafer can form a VLSI composed of tens of thousands to millions of transistors through this "global flattening". For example, the computer invented by human beings has changed from tens of tons to hundreds of grams. It can't do without ultra precision polishing. It is the soul of technology.

Taking wafer manufacturing as an example, polishing is the last step of the whole process. The purpose is to improve the micro defects left by the previous process to obtain the best parallelism.

Today's level of optoelectronic information industry requires more and more precise parallelism of sapphire, monocrystalline silicon and other optoelectronic substrate materials, which has reached the nanometer level. This means that the polishing process has also entered the nanometer level of ultra precision.

How important ultra precision polishing technology is in modern manufacturing industry, its application fields can directly explain the problem: integrated circuit manufacturing, medical devices, auto parts, digital parts, precision mold, aerospace.

The top polishing process is only mastered by a few countries such as the United States and Japan

The core device of polishing machine is "grinding plate". Ultra precision polishing has strict requirements on the material composition and technology of the grinding plate in the polishing machine. This kind of steel plate made of special materials should not only meet the nanometer precision of automatic operation, but also have accurate coefficient of thermal expansion.

When the polishing machine is running at high speed, if the thermal expansion causes the thermal deformation of the grinding plate, the flatness and parallelism of the substrate can not be guaranteed. The thermal deformation error that can not be allowed to occur is not a few millimeters or a few microns, but a few nanometers.

At present, the world's top polishing processes in the United States, Japan and other countries have been able to meet the precision polishing requirements of 60 Inch substrate raw materials (super large size). Based on this, they control the core technology of ultra precision polishing process and firmly grasp the initiative of the global market. In fact, grasping this technology will control the development of electronic manufacturing industry to a great extent.

The grinding discs of polishing machines made in Japan are all custom-made and do not carry out mass production, which directly limits the imitation of other countries; polishing equipment made in the United States is sold to China, and the price is generally more than 10 million yuan, and the sales order has been arranged to the end of 2019, and no order has been accepted before.

In the face of such a tight technical blockade, in the field of ultra precision polishing, China can only carry out self-study at present.

What is the level of ultra precision polishing technology in China?

As a set of high technical requirements of the synthesis process, ultra precision chemical mechanical polishing process must be composed of equipment and materials (polishing fluid), both of which are indispensable. Our national research and development of "CeO2 microsphere particle size reference materials and its preparation technology" has achieved results, and the relevant nanometer size reference materials have obtained the national measuring instrument license and the national first-class reference material certificate. The experimental results of ultra precision polishing of ceria new material catch up with and surpass the foreign traditional materials, and fill the blank in this field.

But this does not mean that our country has climbed to the peak of this field. For the overall process, there is only polishing fluid but no ultra precision polishing machine. At most, we only sell materials.

Polishing process needs to meet the current requirements of electronic industry manufacturing, which can be summarized as ultra precision and large size. With the top polishing material is only the foundation, on this basis, our country also needs to be divided into two steps, the first is to solve the problem of grinding plate, and the second is to solve the problem of polishing area expansion.

At present, the material composition and manufacturing process of polishing machine grinding plate in the United States and Japan have always been a mystery. In other words, the purchase and use of their products does not mean that they can imitate or even copy their products. These are two different things.

What kind of material and technology can be used to synthesize this kind of grinding plate with low thermal expansion rate, high wear resistance and ultra precision grinding surface is the first technical problem we need to focus on. Once this problem is solved, the 60 Inch polishing surface will no longer be a dream. We can never expect to obtain such core technology from others. We have no choice but to rely on ourselves.

Ultra precision machining technology will develop to ultra precision manufacturing technology

To say the least, even if we master the ultra precision polishing technology, we have not reached the final point of machining. Because ultra precision machining technology also includes ultra precision turning, mirror grinding, ultra precision grinding, mechanochemical polishing, electron beam exposure, laser beam machining, ion sputtering and ion implantation, metal evaporation and molecular beam epitaxy.

Ultra precision machining technology used to be used in the final process or several processes of parts, but now in some fields, ultra precision technology is used in the whole manufacturing process or the whole product development process of some parts, including ultra precision machining, ultra precision assembly and debugging, ultra precision testing, etc. the most typical example is the national ignition device (NIF).

Therefore, we should return to the beginning of our article. There is only the origin but no end point. We are still far away from the forefront of ultra precision manufacturing technology. In order to pursue market share and profits, the technology leaders will always improve and improve to be more precise. We are in a backward position and will be beaten if we fall behind, so we need to try our best to catch up.